You're asking the sceptic's question, i.e., still seeing the duck rather than the rabbit.

I think we can know things. We can't prove that we know them in a way that would satisfy a sceptical foundationalist (i.e., a way we could all accept is an "absolute foundation"), because there is no answer that would satisfy such a sceptic. But the real basis of our knowing is only poorly understood by philosophy. It would take me years to coherently tease out what I think about this; it's the Big Question. I think at least part of the answer must come from science, especially contemporary physics, string theory and the like, which, ISTM, is one of the very few parts of modern intellectual endeavour that really takes epistemological questions seriously (academic philosophy long ago largely became an irrelevance when it comes to the big questions, content to sniff around in the mire of linguistic disputes, I blame the positivists for that; most real philosophy seems to be happening in other disciplines). Other parts come from political science, linguistics, psychology, even art and culture. It's a big answer, philosophy helps give the tools to understand why it's an important question, but it's too narrow to supply an answer.

I really recommend you read a book or two about contemporary physics or cosmology, you'd be surprised how not-boring it can be. This is a favourite of mine, when I read it a few years ago I realised that some physicists were asking the right questions, and, unlike most contemporary philosophers, they sometimes have some interesting suggested answers:

http://www.amazon.co.uk/exec/obidos/ASIN/0195126645/qid=1075239968/sr=1-2/ref=sr_1_10_2/202-8215224-4498266

It's a Darwinian account of cosmology, with some very trippy stuff about the multiverse (multiple universes), written by a physicist who also knows something about philosophy and political science.

-- Ian